Delimbing machines for removing the limbs from felled trees are well known in the logging industry. One type of delimbing machine is a stroke-type delimber, such as the LIM-MIT® stroke tree delimber manufactured by Risley Equipment Ltd. of Grande Prairie, Alberta, Canada.
It is often desirable to provide in combination with a delimbing machine means for cutting delimbed trees into lengths in order to facilitate transport and processing. Delimbing machines may be provided with cut-off saws to cut logs into desired lengths while the logs are being delimbed. For example, U.S. Pat. No. 5,628,354 issued to Kingston discloses a tree processor attachment for log porters that is capable of delimbing and severing a tree. This processor attachment includes a trunk advancing and delimbing portion guided in a reciprocal longitudinal movement by a rectangular boom. Movement of the boom is controlled by a hydraulic cylinder with a stroke length of 50 inches, which allows logs to be measured in multiples of 50 inches. A saw blade is used to cut a log from the tree being delimbed once the selected length is reached.
U.S. Pat. No. 6,550,506 issued to Levesque et al. discloses a delimber that uses a butt plate at one end of a boom assembly to determine the length of a log to be cut. Feed rollers feed the delimbed tree until it hits the butt plate, at which point a cut-off saw on the delimbing head cuts a log from the tree being delimbed. This delimber may include a plurality of butt plates located at different predetermined distances from the cut-off saw to allow different lengths of log to be cut from the tree being delimbed. This device suffers from the disadvantage that only logs of pre-determined lengths may be cut, and the maximum log length is restricted to the distance between the cut-off saw and the farthest-placed butt plate.
The '506 patent also discloses a boom assembly without butt plates, in which measuring roller means may be used on the delimber boom to measure the length of delimbed tree emerging from the delimbing head. A log of the desired length is then cut using a cut-off saw. This technique is slow because it relies on the drive mechanism of the boom to advance the delimbed tree. This technique also lacks a means to accurately locate the butt of the log and retain it firmly to ensure that movement is not possible. Any slippage of the log results in inaccurate measurements.
U.S. Pat. No. 6,431,232 issued to Seymour describes a delimber wherein a gripping device mounted to a frame holds the butt end of a tree to be delimbed, while a delimbing carriage movably mounted to the frame traverses the length of the frame to strip limbs from the tree. A saw box including a saw chain is mounted to the delimbing carriage, allowing the tree to be cut into logs of different lengths. The log can be cut to a desired length by translating the movement of the delimbing carriage from the gripping device into a length. The speed of this technique limited to the speed of the drive mechanism of the delimbing carriage. The delimbing carriage must first move to the tip of the tree, removing limbs on the way, then measure back to the first cut, and so forth for trees cut multiple times. Alternatively, after the first cut is made, the remainder of the tree must be picked up and repositioned for the second cut on trees cut multiple times.
There remains a need for cost-effective and reliable means for measuring the lengths of trees being delimbed. There remains a particular need for stroke-type delimbers which include reliable mechanisms for measuring tree length.